Subject: Re: Pinball Displays
From: Clive Jones <[email-masked]>
Date: Sun, 28 Feb 1999 09:56:01 +0000
Newsgroups: rec.games.pinball

In article <[email-masked]>, Duncan Brown
<[email-masked]> writes
>Tony Miklos wrote:
>

<Snip>

>> What about converting the displays to use a LCD display?  Bally uses the
>> 4543 ic which is a LCD driver.  By eliminating 2/3 of the circuitry on
>> the bally display boards, you should be able to drive a LCD display.
>> The only drawback is you need a light source to read them.  Half the
>> price, indefinite lifetime, and no more +190vdc regulator worries, it
>> may have a chance.
>
>Well it would look wrong, of course... but you could solve the lighting
>problem by using a backlit LCD display.  In fact, if you backlit it with
>an orange gas discharge light source driven off of the
>190V....naaaaahhhhhhhh
>

Come on chaps, all the hardware is already in place to substitute the
+190v gas displays with 0.75"-1.0" orange seven segment common anode LED
displays running from +5 volts. (I'd knock up a quick proto, but I don't
have a Bally game up that era handy at the moment)...

Segment drivers:

- replace the resistor running from the MPS-A42 emitter to ground with a
  wire or zero-ohm jumper.

- Replace the current limiting resistor in series with each segment (A-
  G) and the collector of the MPS-A42 with 220-470 ohm 1/4 watt res.

- Remove the current pull-up resistor to +80v (leave open - nothing in
  it's place).

That's the segments taken care of.

Digit multiplexing:

Take the display digit enable data bits (D1-D6 or D7 - depending on the
display type) and feed those lines into a...erm ULN2803 (shouldn't be
unfamiliar to anyone) per display board. Feed the output of each driver
to a small signal *PNP* transistor via the base. Tie the base to +5v
with a 4.7k 1/4 watt resistor. Use the transistor to supply +5 volts to
the common anode of each digit (1 driver/transistor per digit of
course). The current limiting resistor per segment takes care of the
brightness, although, you might want to play around with the resistor
values to play off current vs. sweep frequency (although I doubt it).

Voila! Instant LED display.

Add blanking (not actaully required), a suitable decoupling cap for the
+5 volt power (4.7MFD/16v followed by a 0.1MFD would do nicely) and a
touch of salt, and mix as required.

"LED display Du Jour"

Clive